Many radiofrequency/analog applications make use of low-dropout regulators. For these and other applications, the regulators typically need low device noise and high power supply rejection ratios to operate properly. The main sources of noise contributing to the regulator output noise are a voltage reference, an output feedback resistor divider, and an error amplifier.
In order to improve the noise performance of the voltage reference, conventional regulators are designed to use an RC filter with a high value of either resistance or capacitance. However, because large capacitors consume a large amount of chip area, external noise bypass capacitors are normally used to provide additional capacitance. As an alternative, a bypass resistor with a large resistance may be used with a lower-capacitance bypass capacitor in order to provide low noise with an on-chip capacitor and resistor. However, as with a high-capacitance capacitor, a high-resistance resistor also consumes a large amount of chip area.
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